gfs2: gl_object races fix

Function glock_clear_object() checks if the specified glock is still
pointing at the right object and clears the gl_object pointer.  To
handle the case of incompletely constructed inodes, glock_clear_object()
also allows gl_object to be NULL.

However, in the teardown case, when iget_failed() is called and the
inode is removed from the inode hash, by the time we get to the
glock_clear_object() calls in gfs2_put_super() and its helpers, we don't
have exclusion against concurrent gfs2_inode_lookup() and
gfs2_create_inode() calls, and the inode and iopen glocks may already be
pointing at another inode, so the checks in glock_clear_object() are
incorrect.

To better handle this case, always completely disassociate an inode from
its glocks before tearing it down.  In addition, get rid of a duplicate
glock_clear_object() call in gfs2_evict_inode().  That way,
glock_clear_object() will only ever be called when the glock points at
the current inode, and the NULL check in glock_clear_object() can be
removed.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glock.c

@@ -883,6 +883,7 @@ void glock_set_object(struct gfs2_glock *gl, void *object)
 /**
  * glock_clear_object - clear the gl_object field of a glock
  * @gl: the glock
+ * @object: object the glock currently points at
  */
 void glock_clear_object(struct gfs2_glock *gl, void *object)
 {
@@ -892,8 +893,7 @@ void glock_clear_object(struct gfs2_glock *gl, void *object)
 	prev_object = gl->gl_object;
 	gl->gl_object = NULL;
 	spin_unlock(&gl->gl_lockref.lock);
-	if (gfs2_assert_warn(gl->gl_name.ln_sbd,
-			     prev_object == object || prev_object == NULL)) {
+	if (gfs2_assert_warn(gl->gl_name.ln_sbd, prev_object == object)) {
 		pr_warn("glock=%u/%llx\n",
 			gl->gl_name.ln_type,
 			(unsigned long long)gl->gl_name.ln_number);

fs/gfs2/inode.c

@@ -225,6 +225,10 @@ struct inode *gfs2_inode_lookup(struct super_block *sb, unsigned int type,
 		gfs2_glock_dq_uninit(&ip->i_iopen_gh);
 	if (gfs2_holder_initialized(&i_gh))
 		gfs2_glock_dq_uninit(&i_gh);
+	if (ip->i_gl) {
+		gfs2_glock_put(ip->i_gl);
+		ip->i_gl = NULL;
+	}
 	iget_failed(inode);
 	return ERR_PTR(error);
 }
@@ -816,6 +820,10 @@ static int gfs2_create_inode(struct inode *dir, struct dentry *dentry,
 fail_gunlock2:
 	gfs2_glock_put(io_gl);
 fail_free_inode:
+	if (ip->i_gl) {
+		gfs2_glock_put(ip->i_gl);
+		ip->i_gl = NULL;
+	}
 	gfs2_rs_deltree(&ip->i_res);
 	gfs2_qa_put(ip);
 fail_free_acls:

fs/gfs2/super.c

@@ -1401,10 +1401,8 @@ static void gfs2_evict_inode(struct inode *inode)
 	if (gfs2_rs_active(&ip->i_res))
 		gfs2_rs_deltree(&ip->i_res);
 
-	if (gfs2_holder_initialized(&gh)) {
-		glock_clear_object(ip->i_gl, ip);
+	if (gfs2_holder_initialized(&gh))
 		gfs2_glock_dq_uninit(&gh);
-	}
 	if (ret && ret != GLR_TRYFAILED && ret != -EROFS)
 		fs_warn(sdp, "gfs2_evict_inode: %d\n", ret);
 out: